Sonic altimeter



Aug. 27, J.V A. WIPPERT Y SONIC ALTIMETER Filed Jan. 27, 1958 V2 Sheets-Sheet l Aug. 27, 1963 Filed Jan. 27, 1958 J. A. WIPPERT SONIC ALTIMETER 2 Sheets-Sheet 2 -FIG.2

INVENTOR. J. A- Wpp @r1L ATTORN EY at relatively low altitudes." ,Y

perfomance.

\ V@3,102,261 scherziamo/zuren 4.laines A. Wippert, Burh`ank,Calif.`, assignr 4to The Bendix Corporatioma corporationfof Delaware e Filed lan. 27, `1958, Ser. No. 711,514 p 12 Claims. (Cl. 341-5) f This invention relates to sonic altimetersfror measuring heights and otherdistances by means of sound waves,

Atvari'ousJ times, as` while taking offy `and landing, nit isnecessary for all aircraft to operate near the ground.

Furthermore, certainjtypes lof aircraft, `as helicopters, l

United w'States Patent o often operate near the ground for extended time inter-,r i

vals.4 `In operating,` `an aircraftnear the ground, it is desirable that a pilot` be fcpiite accurately infomed ofvhis altitude.

servations impossible. e systemrwhich lautomatically meaures and indica-teslthe al- Under ordinary conditions, `an vexperienced l pilot can visually observerhis altitude with `suiiicieutaci curacy; however, Avariations in topography maywmake `visu-al judgment of distances quite inaccurzftte.` `Furtherfmore, weatherconditions sornetimesmake visual-ob- Trher'efore, aneed exists for a titud of: an aircraft relativetothe ground, 1lying` It has been previously proposed :to accuratelymeasure and indicate the laltitudeof a low-flyingfaircraft by `trans-l V,mitting a `sound wave, i,.`e., sonic burst, from the aircraftl and observingthe time required for `an echotoreturnf One system `whichrutilizes thispriuciplei of operationxis shown `and described in Vmy, copending United States pat-A ent,'application` Serial,` No. 554,203, ledfDecember 20,

l955,`.nowlPatent no.` 3,038,142, isuued Juneiy 1962.`

Although signicant `advances have been made in' the prior sonic altimeters, certain d-iiiculties ,have remained. l 'i For example, prior sonic al-timeters have been aiected to a' substantialndegreeby `false echoes, `as those'reiiected `l e sonic altimeters have `not measured fthe interval between` 'the -transmissionof a sound wave and the detection of an echo as accurately` `as is desirable, particularly at very" ing` a sweep` circuit having a ,condenserand,twoV charging e, circuits which provides a sweep. voltage. having?, as irst.

`'relatively steepport-ion and arsecond portionthat isuless -r steep than the rst portion but `is steeperfand irnorelinear the vibrating daphragmtypje. ,i t i, y

`In, the normal operation of the system`jth,ef transducer `sound, and electrical energypwhieh transducer, may beo'f 8 issased te transmit @Sonie burStwtQli-tevels t0 y the `eartlrs surface, andlis reiiected back towtheytransdueer `in thefform `of a soriierecho.` ,Upon receiving the lsonic, echo,` the transducer produces an electrical `echo signal, which terminates Va time intervaLthat was, initiated,coin,-`

of Vthe time-interval is therr manifested by'ai meter an indication of altitude.

`The construction and operationofasystem embodying the present inventionfis best understoodby 2considering a `sequence `of operations and `carrying the, description of the apparatus forwardas'thedescriptionfof thefniode `of In B1G. 1, there `is,slijowfri 'vibratorrzli that, when `notexternally lcontrollehl`operates at o e,- secondintervals `to generate both"`apositive`pulse 1'2 and a negative pulse 14; each;` of` 100m`i11i`second duration'.

'Dhe multivibratorV lemmay be triggered bya `received echo signal to generate the lOIO'fmi-llisecond pulsefaft 4less 1 ow altitudes, and` at-alti-tudes near thefupper limit Iof the altimeters. El i An object of the invention is to'increase the immunity 'of a sonicaltimeter `tospurious]signalsand false echoes. Another lobject is to provide i a 'Sonic altimeter which transmits a sonic burstI of `variable durationin accord-ance with the last-observed altitude, to'whereby form a longs,` 2

duration sonic burst which is more immune `to spurious signals `when the distance to `be .traveled is long, and to "form a sl'iort-duration` sonic burst-which'does not inter- Y fere with arrapidly returning echo when the distance to be traveled is short.` e l Still anothenobject is to provide `an improved `means for measuring the time interval between sound transmise .sion and echo detect-ion. "t

than 'one-second intervalsfgifl'he waveforms from theV 40` multivibrator 10including,` pulses 1,;2 and 14', are shown respectively in FlGS, `2A 2B. The` iastable, multivi bratorlll maybe the typeushown and described begin? "-ning onpage V171 "of volume `19 of theRadiation-Ltabora'? i Y entitled Wavefrms, u ,publishedeby V,tories 'Series,l

The ,output ,line ,161 frorntlie multivibrator 1li, whloh f f carries the pulse 12,'is eonnected'tda variable'epulse .lgeng A still further object is `to providefina sonicaltimeter,` improved means to indicate that the aircraft is Aoperating at a safe altitude,` f n t Briefly,` the present invention Ais an echo distance system for measuring dista-nce or altitudeby transmitting a sound wave, and determining theintervalrequiredv for an echo to return to the point oftr'ansmission. The system incorporatesseveral features `which-result `in improved` pulses of different durations depending upon the altitude Aof the aircraft, wherebyiat low altitudes echoes which would otherwise return prior to the termination of the transmitted sound pulse are not lost, but `sound `pulses `of a longer `duration are provided when a greater distance i `i's'jto be traveled.` i

` Another feature is One feature isthetransmission'rof soundanqimproved means `for measuring 1` the interval between transmission and detection employ t ,e eratorfls. Therfunction ofthe" variable fpulser generator v i `1,5 to'providepulses 20,` of variable length, `which determinethe duration otthej burst of sounltl,transmitted by `the system. "Thegfduratiomof" the pulses 20 ivariesfas ing s'ystemis` low, the sonic burst; fvshort `durationand does notfinterfere withithe echoslllowever, when the i aircraft is` ahighatv altitudes, the 1sonic Vburstisl of a long duration `and 1produtesl an Vgecfho `that in thefpresencegof 'spurious signals. l 'Ihe variable t pulse? rgenerator 13 "receives a co is easier to, detect potential varies with!f the; last, ,'indicated14 ground, and the plate is connected through. a v`load re'.- sistor 2S to positive`lpot`e"`ntial,` so Vthat the `voltage `at the plate 'of the tube Z-tf` `varies `inverselyas thealtitude signal injthe" line VThe plateyof the `tube Z4-"is connected through the resistors 3d 'and 32 land condenser rameau-127, rises l e tin'uous positive potentialqfromnaline `22 the amplitude ofwhi'ch` e lhll'lld.' ThlS i 5 V,altitudepotential is appliedto the-fgridof a tubel24from v .the Vline 22. througha resistor ,26. `The grid is also i connected'througha resistor 26 `tonegative potential which .biasesthe tube togcnt-ofl when the altitudepotentialyis "VIZeroL The fcathode of `the*tubeMis lconnectedto i "ft-321; miie une .16; si, ma

the

The fdelayedpulsee tonthe'sweepcirouit through the line which is conduringftheperiod olf pulse I12. Thereafter, at the oej currenceo'f the rtrailing edge of the pulse -12, the condenser-A341 discharges to produce a" voltage having a wave? form :37 "la lshown'inl/FIG.l 2'C,'""at therjunctionV 35 be? for ashort intervaluntilVV thevoltage att' junction 3:5` is restoredby current through resistor 30,' the vtime the condenser 34 is chargedv j nected to the 'grid of a tube7f1. I e and cathode serially connected with a condenser 72 vand adiode 74. The condenser 72' isqalso connected to a iirstcharging circuit, including ya diode 76 and avoltage i divider consisting of Aresistors .86 and7 `cor'inected be-V tween the positive source ground, and .to a second` charging circuit includinga. resistor 80 and thepositive I source." The gridoiuthetube 711is connected .through a .The tube 71 has its plate biasing resistor y82 to'negative potential, and thecathode lof thetube is connected to the variableA tap of a potentiometerSifl which is connected between groundand being'fdetermined thythe potential 'at the plate of the Y tube 224.` Thev platel 'of' the tmbe 36 is connectedV to a source 'of positive potential*throughwa-'load-resistor :38; l

" therefore," during the interval thattlie ltlub'e is' cut' fori, the' pulse y (FIG, 2D) :isforrned at theiplate of the tube 36;

Y 'or-souris, the .duratiqaftof the @puise zu varies as the wie i agefonthe'plateiof tubeZfi, which in .turn depend's'upon the vlast indicated altitude; -fthereoreg A'the' duration of the pulse- ZOmaybe seengtovary las the last indicated altitude- Thebpulsezt)isappliedfthroughfa Vcoupling condenser 452 l to a gating -larnpliiier 44,? Whioh isf also connected to a 1i-kilo cycle/rseeorrciA oscillator 46 Th-elgating amplier "intervalgof pulse. 20'; V*The resulting output yfrom the gat` ingafamplier 44, comprising a periodic burst of. 3-

' in parallelwitha portion of the potentiometer 84. rWith the occurence ofthe tn ailing edge'ofjthe .pulse Gr the tube 71 is cut olf, Jand the condenserfg72i' begins to charge tor 80; and the diode 76 and resistors 8 6and78',

produce sonic bursts.

Y The. soniofburst produced bythetransducer lS may Strike "object,y as the'earth" and forni 'an echo which is reilectc'd 'he 'intervalbetweenv the time-fof the *lnepievius sweep Signal isefaunatad'bg/ the leading fedgeof the pulse 12an'df sw ep signal isinitiated by ng edgefofthepuise 124 5S is connected; through a 54,1.andsthrough aline GSoajsWeep circuit 66.

signal includes 1a positive lpulset plate from being drivenjpositive vb'ythe vsimultaneous' application' 'of the pulseto'the platethnough resistor 64.. "After-.the'pas'sa'ge of'theipositiveikpulse 69, the tube 62 is cut o if, and ythe plate of the tube 62, goes positivel to forni pulse G1' having`adelayed :rise `as shown in FIG.

' The vpurpose@if.delaying 'the vrapplication vof the `pulse to be metered before the sweep circuit elecho signal is measured to indicate v-lthe esioundha -t'rs a.'veled.' In general, this' sweep signal 'attains duringV the interval `Upon application ofjthe lpulse '12v'to'the condenser 5 6, pulsev 'isjdifferentiatedtofformla signal, las shov'vnin`- 2F,\7at t1he:gridof--the' tiibesGZ' v'The Vdifferentiated A y ,coinciding intime Withtheleading'edgeoflthepulse A12,an`daf negativefpulse r`'l'.t), coinciding with the'tnailingedge of the pulse 12. The positive'lpulsef69cau'ses`uhe'tube 62 to conduct upon initiallfy receivirfglthe pl'llsel2;,1andV temporarily'preventsthe negative potential and serves sweep circuit. v-

asa' zero adjustment Vfor the At a time 'when thedelayed vpulse Giv 'is appliedtoithe grid of theltube 71, the tube lisrendered conductive, 'and the condenser X72 discharges through the. tube v71 and the diode 74." The :diode is provided to -allowfthe condenser to discharge'rapidly byproviding alow'irnpedance path through the two paths, respectively including: the resisf` Ifhe ioperationof charging alcondenser'through aresistive circuit conventional to form a sweepvoltage; however, because the condenser ohargesin Aan exponential yfaslii'on,";o1 1ly the vinitialportion of the generated sweep voltageapproaches linearityl The plurality of'cha'rging Y current paths in sweep circuit .66 provide a sweep VoltageV has a steeper slope in its'lower portion and which Y'is 'more linear in, its upperportion and' also has :a steeper 'slope in itsupper-.portion than doe'sjacomf/ entional Sweep circuit having only one charging current'path;

rue antinfeh'arging v period @f thegcndenserfjz through. both theresistorlttl andthe' resistojrq-fand diode 76. Theresistorhas-antuchl lower vresistance than resistort s othatfdespite .the current bypassed to ground through the resistor 8 6, thecondensej'l isc'zhar'g'ed much .5 .upperportionf of thejswe'ep; .curve would ibe substantially desirable in fa'soni'c altimete'rtofprovide high. sensil l tivity `at lowlaltitudes, while maintanng-a lesser but apun as indienen bythe dotted im@ in lrojzrr.A However, i Vwith thegfullpotential ofxthe positive source Vapplied through 'the fl n'g-h-resistance-` resistor 80, charging current v:continues Ino flow to the condenser at a slo vv"'1b1 it subs/tan#V j tially constantina-te to'y produce thesec'ondgportion 92V of the sweep ycur ve having aslopefless 4than that of the f portion 88, but relatively constant The diode76 prl i vents current from the resistor Stl'heingbypassed through theresistor 86j4 f Thus,l the niultipathcharging circuit 'produces a sweepv f vpotential having fasteep slope in uhelolvver portion', which preciable `slope 'throughout thefupper range so that useful vindications `are still produced atrelatively highv altitudes.

`As'aresult of thesweep-pattrn of FIG. 2H, the pointer of meter 9' may'move Vthroilgli the rst half lof its' range `during"the'fiirst `SO-foot rise invaltitude to. give extremely accurate readings near the ground, andmove substantially linearly .through the second halfl ofits range during a subsequent risefro'rn 50 feet to y300 feet.'7 As is customary.. e

`in altimeters, the scale of thefmetergis jg'areferahlyfcali-V brated to t the sweep pattern and read out thealtitude directly Virrfeet ory rneters;v i

Simultaneously with the developmentof thesweep volti- Y age ((curvoZI-l) the swee"rntzirctii tj6o, the'sonic 'burst Asignal 45. The `amplitude discriminator circuit 9d functions to preserve the echo signal by -allowing it to pass While eliminatingthe burst signal by `not permitting `it to pass. i i Amplitude Dircrmz'nazor Immediately prior to the tirnewhen the burst signal d is formedto produce the sonic burst, the negative pulse 14 isapplied over line 20% through resistors .98, 100 and 102 to negatively charge a condenser 11.2,V as indicated at 146 in LFIG.` 2J, and drive 'the grid of `a tube 104 beyond cut oit until the occurrence of the burst signal. The cut-off level is indicated by the dotted line in FIG.

2J. When the burst signal 45 appears on the line 92 from i the output circuit 48, it is applied to the condenser "106,

and during positive half cycles of the signal the anode of the diode i110 is driven positive through the capacitor v1(96, causing the diode r11@ to pass current and charge the capacitor 186. IDuring, negative half cycles of the burst .s1gnal 45 in the line 92, the diode 110 presents a high impedance to the negative-going signal and therefore does not conduct. As'a result, the capacitor 106 issufficiently charged to clamp the positive peaks of the burst signal at essentially zero potential.` The wave form of such af clamped signal is shown at 45a in FlG.`2l, as lit appears ing systemduring the interval of the burst signal, and to f reduce the sensitivity of the receiver foran `interval im`A rnediately following the burst signal. e; To prevent spuriousV at the anode of the diode 110 following the direct current negative pulse .14a applied through the resistors 98 and 100.-,` The diode 1% prevents the junction of resistors 98 and I14.10 from ever going positive in response to any positive potential that may occur on the line 201i.

With regard to the burst signal 45 and the echo signal 5.1, the resistor 102 and `the capacitor `112 form anattcnuatingcircuit to reduce the amplitudes of these signals resultlng 1n a Waveform as shown in FIG. 2]'. From the Waveform of FIG. 2l it may be seen that the echo signals 5=1b attain a higher voltage level than the transmitted `burstsigna'ls ib; therefore, ordinary amplitude selection may be employed to preserve the echo signals and eliminate the transmitted burst signals. Such amplitude selec- I tion is effected by the vacuum tube `104i which has a cutfoiflevel (the dotted line in FIG. '21) below at least the positiv-e peaks of the echo signal and above the positive peaks of the burst signal. `It is important to note, with reference to FIG. 2J, that it is necessary that the burst signal 45h be `completely`below the cut-off level of the tube 104, but it is not essential that the echo signal51b be completely above the cutoff level. The burst signal should be completely blocked, `but it is not necessarythat allof the echo signal get through.

` The burst signal istherefore suppressed, and thefecho `signal is passed fromv the amplitude discriminator 9o `through a condenser 113 to a band-pass iilter 115 which eliminates certain spurioussign-ais 'bj/.frequencyl selection. The output at `the plate of tube 104 is shown in FIG. 2]. It is important to note that the tube 104 refmans cut off during the burst signal, regardless of the duration of the burst. The output from the lter 1115 is applied to an amplifier 117, which is turnwcoupled `to an amplifier 119.

Gain Control `When the burst signal is transmitted,v echoes` may be `reflected back to the system from lprourberances upon the aircraft, and as a result, false indicationslmay be derived. Therefore it is desirable to disable the receivor false-echo signals from being .detected bythejsys-tem,

a gain control circuit is provided which initially rendersl the receiver blocked, then'grlad-ually increases the sensi-` tivity of the receiver so that the receiver becomes more"` sensitive with the passage of 4time from the` instant i the sonic burst is transmitted. It is desirable that the, degree of sensitivity of the receiver be somewhat proportional to the :altitude of the aircraft;l

` The timefvaried gain ofthe receiver portion of the system of FIGLl is effected by the time-varied gain control circuit 114. The circuit l114i includes a tube I11.6, the grid of which is connected through a resistor `118 tothe plate of the tube 106i.` The tube `116 has acathuo-de which is y connected through a voltage-dividing' network `11.2() so as to receive a negative potential. Normally, the tube .L16V is nonconducting; however, during the IDO-millisecond interval immediately prior to a sonic burst and during the interval of a sonic'rburst (when the tubelA iscut e oii), the high positive voltage at the ,plate of the tube 1614i (FIG. 21') `drives the grid of the tube i116 lSuiiiciently positive to render it conductive. `The tube 116 "therei fore conducts for an interval in part determined by they duration of thefsonic burst.` `Because the sonic burst varies in duration With indicatedfaltitude, the interval during 'which the tube 1116 conducts also varies with altitude.` l Conductionby the tube `116` produces a. currenttoV negatively charge a condenser 122 which is in,4 shunt i with a resistor1'24i.` The discharge of the condenser 122 occurs through the resistor 12.410 produce arising voltage 125l which starts immedietely following the sonic burst, as shown in FlGJK. i

The voltage developed on the cndenser 122, as shown in FIG. 2K is applied to a line 1126 and ser-ves to con-` trol the sensitivity of the receiver .portion oi the systenr` by` variably biasing the imputs to thearnpliflers`1'1'7 and 119 so that the` sensitivity; of the` receiver` gradually increases from the termination ofithe sonic burst. Of A course, the strengthof the echo signal is: inversely propor-l tional to the altitude; therefore, at low altitudesthe echo signal strength is greater, and the sensitivity of the re-V ceiver need not be as great'to detect echoes,` as` at high altitudes.

Y The receiver portion of the system shownmay also be subjected to considerable noise; therefore, it `is desirable to provideA lan automaticigain control to vary the gain `of the receiver in` accordance with the strength ofthe `received signal. `This function is effected by the automatic gain control circuit 128i. This circuit 12S includes a tube 1311, the grid of which is connected j through `a resistor 132and a condenser 13'4 to the output of the ampliiier i119. `As a result, the conduction of the tube i is controlled by the `voltage appearing atnthe` output from the amplifier :1.19, andthe `voltagelat the plate of the tube 13ti`|thereforevaries accordingly, and

is applied tov the line 126 to effect gain cnntrol of `the ampliiiers I117 andl119in conjunction with the 'output from the time-varied gain control circuit-1114.

The signal applied to the automatic gain control circuit 123 from the amplifier 119 is an alternating-current sig.-

, nal; therefore,to provide steadycontrol of thestube 13() and producel a gain control signal, it is necessary that the AC; signal be rectiiied, as by diode 136. .The diode 136 is connected at the junction point 141 between the resistor 132 and `the condenser 134, and is also connected to a` voltage-dividing network 13S which isconnected between t ground and negative Tpotential. A resistor `i is also e contacted between the junction point 141 and the voltagedividing network 138. `AA condenser 142 is connected be'- tween the grid and cathode ofthe tube 130.

In the operation of the automatic` gain control circuit, Y during the period when thetube 1014i` iscompletelycut y .Thepulse 1581s c s,1o2,26,1

'put fronrthe ampliienllQ; therefore, the tube 136) tends to.,become cut olf, thereby enabling the line 126 to bei` corne less negative andrender the amplifiers 117 and 119 yeryfsensitive. When the tube104 is again rendered con- .c ductivethefampliers 117 and 119 would thenfremain fvery ,sensitive and could' provide a noise signal adequate v i gain control circuit .114,to. renderthe receiver insensitive toy false .echoesf and noise signals occurring immediately after. the sonichurst.' l

i t VfUlreshOld Circuitl signalhas been 'arnpliiied by the ampliliersI 117 and 119, it is applied to a threshold circuit 1416. The

rsignal,`from the ampliiier 17,19 israpplied through. line 121 and resistor y148 tothe control grid of a thyratron 1S@ Iin the threshold circuit. The plate ofthe thyratron 150 is connected through'a'load resistor 152 to positiverpotentialwhile the'cathode'fis connected through a. resistor 154 totground. j `The second grid in the thyraton d. is connected throughfa, current-'luniting resistor 156 to ground. Thejthyratron 1,50, isnormally cut'V ofi; therefore, the loplate'is'positive.. Upon lreceiving the amplified echo signalthroughthe'resistor 148, the thyratron 15) is rendered conductive, thereby producing a negative pulse 158 at its lplateas 1acondens"er 157 connected between the thyratron plate flandfground is"discharged. The waveform ofthe v voltagev at the plate VofL-the thyratron 150 is shown in @In the operation of ythe receiver portion vof this systermas previously described, the tube 104 (in the ampli-l rudediscrirni'nator',9'6)y iscompletely cut oir prior to the transmission' ofthesonic burst. At the time when `the tube`104` is 'cut off (point 1419 in FIG.'v 2J), a positive voltageis: formed at the plate which is applied through ``the condenser 113 tothe band-pass lter 115. This change in 'voltagemay be ofy suicient magnitude to ring the iilter ooi;(imr nediately lprior `to yand during the transmission y of thesonic burst, as shown in FIG. 21), thereis no outconnected diode 1- 72 and-condenser 174 in thecinformation-monitoring circuit 171, The condenser 174 isrconnected to ground. Thefjunctionfpoint 175 between the diode 172 andthe condenser 174 is connected toga source of positiver voltagethrough a resistor-176, andto the con- Y trol grid ofatube 1.78. The plate of the tube 17S-is con-l nectedto positive potential, andthe cathode is connected through a relayv 180' and a resistor 182 to ground. The

' contacts .184 of the relay 180 are serially connected with 's sipated through the diode 172 and resistor 154, and there`V a light bulbf186 between positive potential and' ground.A

During 'therintervalafter a sonic burst is transmitted, thevcondenserl 174 inthe monitoring circuit charges throughthe resistor 176 toward a level at which the tubev o 178 becomes more conductive; however, when the thyra'-v tron150 conducts, the charge on thefcondenser174 is dis-A fore. theitube 178 becomesless conductive.v However,

when no echo lsignals are received during the period of a few seconds, the charge on theV condenser 174 becomes adequate to drive the tube 17 8 suiiiciently conductive to energize the relay 180 through the resistor 1S2,close the c contacts 184,and illuminate thel lamp' 186. As a result,

f the lamp 1t6is illuminated during intervalsV when the aoy altitude is beyond the range of the altimeter.

signals as well as other visual indications. 1 v

.Altitude Indicator Circilz'ts The pulse 1523 from the threshold circuit 146 is also applied to a flip-nop circuit 18S ,which is'in turn connected to a gate circuit 191i. The flip-dop circuit 188 may comprisea single-shot multivibrator as shown and described in the above-referenced book. The gate circuit 190 may talce various forms, one `ofwhich is shown land described i 11'5fand produce an lalternating signal that passes through the'ampliiiers 117 and 119 and triggers the thyratron 150;

' l.Due tofthe delay incurred by this transient in the lter 115, .Y l the danger of 'false triggering occurs during the interval of u v v thel pulse 12; therefore, the pulse12 is employed to render the thyratron IStltemporarily inoperative. The pulse 12 *vis-applied to a tube-160 in the threshold circuit 166 through fa ,line 162.' The tube 160 has a vcathode connected to a lvoltagedividing network164 so 'as to receive al negative tween'a diode 166anda resistor 168. The diode' 166 and the AresistorV 16S are connected e'between'the line 121 and ""potentialj :and a plateco'nnected to a junction point bev ground. During the'period of the.pulse`12`,the grid of o thetube 160'is'driven positive, .therebyrendering the tube 1601conductive4 :through the.. resistor 16S` to drive the line @"121 'more negative through the diode 166. As a result, y1 )spurious signals which appear upon the line 121- during the interval of the pulse V12 are not capable of triggering the thyratron 150 in to a false operation. v 1 `The operation of the thyratron 150`in conjunction with to meter the ,present altitude; avmonitor circuit is con- ,trolled to indicate that the system is receiving altitude information; rand' thejastable multivibrator 10 is triggered l -tostart another cycle of operation.

M anitoifngl 'Circuit o y appliedthrough aline17t) to a serially# promptly terminates' anyremaining portions yof the echoi `-thecondenser 157 to form a'neg'ative-pulse. llShas sev'- f f 'eral eifects. j- The amplitude of the sweep voltage is sensed v lin the above-referenced patent application. The flip-nop circuit 188 functions to render the 4gate circuit 19t) operative during a precise interval to pass .a signal indicative of the'present charge on the condenser 72. Of course, this charge constitutes' thevsweep signal, and the :amplitude thereof is indicativeof altitude. .The altitude-indicating signal sampled byv thel gate circuit 190, as shown in JFIG.

2M, is stored upon a condenser 194 which controls the conduction of the tube 196 -in the meter circuit- 192. The tube 196 is connected in alcathode-'follower fashion, having a plate connected to positive voltage 1and .a cathode connected ,through a resistor. 197 to negative potential; The cathode of the tubej196 therefore follows the voltage at the grid of the tube to provide a voltage indicative of altitude. The voltage'a't the cathode of the tube 196 is ap plied through avariable resistor-,198 andthe meter 9 to ground; As a'result, the voltagedeveloped on the con' y denserf194 is manifested by the meter 9, Vindicating the altitude. v

'c o Initiation of New Cycle The negative pulse '158 is' applied tothe multivibrator 10 through a diode 159 and triggers the multivibrator to v'iorrn'lla pulse 12, thereby starting another cycle of operation. 1t is'irnportant to` note that a new'lpulse 12 is initi-` ated immediately lby the pulse 158, .and the new pulse 12 produced'signals 51a, 5111,151c,l in EFIGS. ZI, 2J and 2l.

The pulse 158k occurs as soon 'as'.the amplilied pulse 51e builds up suiiiciently'to trigg'erthe thyratron 150, which v tiring may Abe during the 'rst vor a subsequent positive halfacycle of the ampliiied A.`Cpulse 51C.- However, the sweep voltage..(FIG. 2H) continues for a short time following initiation iof fthe new pulse 12 to insure operation for the altitude indicator circuit.

v To consider the over-all .operation of the system in gen eral, .and thereby `surnrrrarire the previous` description, it may be seen that the multivibrator 10 operates to provide pulses 12 vandzlri. The operation of the multivibr'ator inthe absence of received altitude information will be at onesecond intervals, and during' receipt of altitude The use 'v I of the relay mayalso be extended toprovide audio information will be more frequentand determined lby the The pulse 12 from (the lengtliof which is proportional to the indicated altitude) which is applied to a gatingramplier 44 to gate a burst :of oscillations from the oscillator 46 to the output -circuit 48, andthus to the transducer S. With the transmission of the lsonic burst, a timing operation involving the charging cifra condenser is started to determine the distance traveled bythe sound Wave. transmitted sonic burst is detected by the transducer 8,

applied through the output circuit 43 `and the line 9-'2 to the amplitudediscriminator `96. The amplitude discriminator 96. functions to render the receiving system inoperative duringthe transmission of the `sonic burst regardless of theduration of the burst which varies With thelast indi-` cated altitude. From the amplitude discriminator 96 fthe echo signal is applied to the filter 115 to be iiltered and t thereafter amplifiedby amplifiers 117 and 119. The signal is then applied to the threshold ci-rcuit 145 "to develop.

. improved .sonic altimeter fully capable of achieving the objects herein previously set forth. t

Although for the purpose of explaining the invention particular embodiments thereof have been shown fand de` scribed, obvious modifications will occur to a person skilled in the art, and I donot desire to be limited tothe exact details shown and described.

I claim:

1. An echo distance-measuring device comprising:

means for successively transmitting lbursts of travelingV Wave energy; detecting means for detecting an echo :of each said burst; indicating means for manifesting distance; time-measuring means responsive to each transmitted burst and its echo for setting said indicating means in accordance with the duration of the echo interval between the transmission of each burst and detection lof the echo thereof; v and means for controlling the duration 'of each` said burst in accordance with the duration `of the preced-` ing echo interval zas means; said detecting means including: a transducer for'converting said echo into an electrical echo signal, amplitiernieans for amplifying said electrical echo signal, automatic gain control means for regulating the gain of said amplifier means in accordance with the signal strength received by said amplifier means, and means for reducing the Vgain of said amplifier means during the transmission of a burst of traveling Wave energy. 2. An echo distance-measuring device comprising: means for successively transmitting bursts of traveling wave energy; p t detecting means for detecting an echo of each said burst; indicating means ffor manifesting distance; time-measuring means responsive to each transmitted burst and its echo for setting said indicating means in accordance with the Iduration of the echo interval between the transmission of each burst and detection of the echo thereof; means for controlling the duration of each said burst the annivibrator 1o is p applied through the variable pulse generator 68 to develop appulse The echo of the indicated yon said indicating p control meansfor setting the sensitivity `of said detecting means ata low sensitivity leyel,` to thereafter gradually increase, said control means functioning during the transmission of arburst; and

meansl for varying the duration` of `said`low-"sensitivity level inaccordance with the4 duration of said interval. 3. An echo distancemeasjuringf `device comprising; means for transmitting a burst of traveling wave energy; detecting means for detecting lan echo of said burst; indi eating means for manifesting distance; means for setting said indicating means `in accordance with the duration of the interval between the transmission of said burst tand detection of said echo; control t means forl setting the sensitivity of said detecting means'` 'at a `low-sensitivity levl,.to thereafter gradually increase, said control means functioning during the transmission tof a burst; and means for varying duration lof said low-sensitivity llevel in accordance with the duration of said interval.` r

4. An echo distance-measuring device-gcomprising: means for transmitting a burst of traveling Wave energy; transducer means for detecting said echo to form an electrical echo signal; amplifier means for amplifying said echo signal; automatic gamcontrol means for regulating the gain of said amplifier means in accordance with the signalv strength received lby said `amplifiermeans; means for reducing the gain of said amplierrneans during the transmission of a burst of traveling Waveenergy; in-dicat- 1n accordance with the` duration of the interval between the transmission of said burst and `detection of said echo.`

5. A sweep generator comprising: 1a capacitor; a 4high potential charging circuit having highimpedance; a loW potential charging circuit :having low impedance; means connecting said high potential charging circuit to said capacitor to charge it; means inclnding a unilaterally con ductive device connecting `said low potential changing circuit to said capacitor to charge it; said unilaterally conductive device being poled to conduct charging current from said 10W potential charging circuit to said capacitor and prevent reverse flow, whereby said capacitor is charged from bot-h `said` charging circuits until the capacitor potential rises to `the `potential of said low potential charging source and thereafter from said high potential changing circuit only. p

6. Apparatus according to claim 5 in which said thigh potential charging circuit comprises a potential source and `a high impedance conductive element in series therewith, and said low potential charging circuit comprises -a passive voltage dividing network `connected in shunt to 1 said source.

7. In an echo distance measuring* device having'means f for transmitting a burst of traveling wave energy and means for receiving an yecho of said burst, indicating means lfor indicating the time interval between said burst and said echo comprising: means for generating a rising voltagethavin-g -a first portion rising substantially linearly from a first level at the instant `of transmission of said burst to Va second level Within a fixed time interval and a i second portion rising substantially linearly fromlsaid rise `of said rising voltage from said iii-st level at the time of said reception; said rising voltage generating means comprising a condenser, the Ivoltage across which constitutes said'rising voltage', and` variable-resistance charging means variable in response to an increase in the voltage across the condenser to saidsecond level for charging said condenser at a rapid Irate to said second level' and at a slower rate above said second level.

- connecting said tirst charging means `to said condenser.

Apparatus according to claim-7 in which said charg-i ing'v means comprises: Va first charging means consisting offa variablefvoltage,"source the maximum voltage of which correspondssubstantially, to said second voltage level, andfhavin'g" relatively low fresistanceg' a second charging means connected in. parallel to said first charging meansfand consisting of a voltagek source of voltage substantiallyhigher `than said vmaximum voltage and having relatively high resistance; and means for electrically isolating said 4first charging means `offsaid condenser'in responsetorise of. the 'condenser voltage above said max- :imum Vvoltage.`

9. Apparatusfa'ccordin'g to claim 8 in 'which said isolating means comprises a unidirectional conducting device 'indicating devicel connected to said storage capacitorg' fmeans responsive gto each transmitted burst for generating a potential rising at a predetermined tim rate from a predeterminedy base value; K K gating means.' actuated by eachy detected echo for'con'- necting said voltage-generating means to said' capac- Y itor .tocharge' said capacitor to the potential corre- 'sponding to thetime interval between said echo and the burstthatcausedit; y

and means for determining the duration of each of said bursts in accordance with the, magnitude at that time of the potential stored on said capacitor.

4, `12.."Ecl1o distance-measuring apparatusk comprising:V

means adapted to be triggered to generate a vfirst voltage Y erator' controlled by saidv second pulse and.4 responsive thereto to delivera voltage of xedbase'value throughout the duration of said ysecond pulse and a rising .-.Voltage beginning at the end of the second pulse; burst signal-transmittingmeans controlled by said rst pulse for transmitting a burst of traveling Wave energy kat thel trailing end of said rst pulse; echo-receiving means'f'orgenerating a trigger pulse in response to reception4 of an echo; means responsivevto said trigger pulse for triggering `said irst pulse-generating means to generate ay new' iir'st pulse; t

and means responsiveto said trigger pulse for indicating y l.

the instantaneous magnitude of said4 rising Vvoltage.,k

` References Citedl in -the ile of this patent UNITED STATES PATENTS .2,083,344 .rsrewhouse` June s,y '1937" 2,167,492 SplOule g]u1y'25,"1939 i 2,337,905 Livingston Dec. 28, 1943 2,427,523 Dolberg Sept.v 16, 1947 2,446,960 Seebingel' v i Allg. 10, y1948y 2,466,539 Evans Apr'. 5, 19491'v 2,519,898 Gardener Aug. 22,1950l 2,542,983v Beatly l` "Fb. 27, 19511 '2,551,595 y Grieg k May 8, 1951 2,890,437 Y Dudley lJ'une 9, 1959 l2,903,684 Jaffee' et al. Sept. 8, 1959 '2,946,050 Wathen July i9, 1960 2,981,942 Gross Apr. 25, 19161V l FOREIGN PATENTS 'l Y France j ty 14, 1956 

1. AN ECHO DISTANCE-MEASURING DEVICE COMPRISING: MEANS FOR SUCCESSIVELY TRANSMITTING BURSTS OF TRAVELING WAVE ENERGY; DETECTING MEANS FOR DETECTING AN ECHO OF EACH SAID BURST; INDICATING MEANS FOR MANIFESTING DISTANCE; TIME-MEASURING MEANS RESPONSIVE TO EACH TRANSMITTED BURST AND ITS ECHO FOR SETTING SAID INDICATING MEANS IN ACCORDANCE WITH THE DURATION OF THE ECHO INTERVAL BETWEEN THE TRANSMISSION OF EACH BURST AND DETECTION OF THE ECHO THEREOF; AND MEANS FOR CONTROLLING THE DURATION OF EACH SAID BURST IN ACCORDANCE WITH THE DURATION OF THE PRECEDING ECHO INTERVAL AS INDICATED ON SAID INDICATING MEANS; SAID DETECTING MEANS INCLUDING: A TRANSDUCER FOR CONVERTING SAID ECHO INTO AN ELECTRICAL ECHO SIGNAL, AMPLIFER MEANS FOR AMPLIFYING SAID ELECTRICAL ECHO SIGNAL, AUTOMATIC GAIN CONTROL MEANS FOR REGULATING THE GAIN OF SAID AMPLIFIER MEANS IN ACCORDANCE WITH THE SIGNAL STRENGTH RECEIVED BY SAID AMPLIFIER MEANS, AND MEANS FOR REDUCING THE GAIN OF SAID AMPLIFIER MEANS DURING THE TRANSMISSION OF A BURST OF TRAVELING WAVE ENERGY. 